There is a need for high-speed cost effective optical transmitters which can operate as parallel optical communication data links. Prior analog communication systems have evolved to digital systems to satisfy the demand for the transfer of greater volumes of information. To meet this demand, advances have been made in transmission and in signal production of optical signals.
The preferred method of transmission for telecommunications is now optical fiber due to the increased bandwidth capacity and lower signal attenuation as compared to traditional copper networks. Optical fibers are thin filaments of drawn or extruded glass or plastic having a central core and surrounding coating that promotes internal reflection. A typical single mode fiber has a core diameter of only 10 microns while a multi mode fiber has a core diameter of 50 microns. The optical fibers are disposed within a connector, such as a commercially available MT optical connector, which is attached at one end to a waveguide with the optical fibers in alignment with the core region.
The preferred method for signal production for digital optical communications is by laser, and in particular semiconductor lasers. For example, vertical cavity surface emitting lasers (VCSELs) emit a coherent, collimated unidirectional light beam normal to the surface in which they are formed. The nature of VCSELs (and semiconductor lasers in general) is that the optical and electrical characteristics between each device vary slightly. The back or bottom surface of the VCSEL is usually attached to a mounting substrate and the output is emitted from the top or front face. Typically, an array of VCSELs are aligned so that each individual laser is positioned proximate to an input port which runs along a horizontal line in the front face of the optical connector.
In order to achieve high-speed cost effective optical transmissions, there is a need to efficiently couple a light source to an optical fiber. In aligning an array of VCSELs with their corresponding optical fibers it is desirable to ensure that each of the fiber ends is in precise alignment with corresponding lasers so that the optical signals are received with minimal distortion and/or attenuation. Alignment of the optical device to the waveguide within the optical connector usually requires manual or active positioning. Typically, alignment involves sub-micro meter accuracy, performed manually by skilled technicians using microscopes and high precision manipulators.
To simplify the alignment process, assembly frequently involves a passive guide approach. U.S. Pat. Nos. 5,179,609, 5,913,002, 5,574,814, 5,963,691, 6,130,979 describe various passive alignment systems for transferring optical signals from the light emitting device to the optical fiber. For example, U.S. Pat. No. 6,130,979 describes the use of alignment pins which are inserted within matching recesses for positioning the fiber optic cables relative to a laser array.
These passive alignment techniques are typically employed manually by the skilled technician just prior to the application of an adhesive to secure the fiber optic cables to the laser array. Unfortunately, the existing techniques employed in connection with passive alignment systems emphasize the importance of achieving alignment over all other operational requirements. If the alignment was successful as determined by a post-adhesive test of the connection, then the component has been successful built and the technique achieved its purpose. If, however, the alignment was off, either due to manufacturing tolerances or assembly variations, and the component fails a post-adhesive test of the connection, then the entire component must be scrapped. In addition, because of the differences in cure time for various adhesives, the passive alignment systems must remain in place for the entire duration of the relevant cure time.
While existing passive alignment techniques for aligning an array of VCSELs to their corresponding optical fibers have decreased the rejection rate associated with assembly of these components, it would be desirable to improve other aspects of the assembly process without sacrificing the gains realized by incorporating passive alignment techniques in the assembly process.